The present invention relates to a cap, a button group and a method for forming a button group, and more particularly relates to a cap, which is one part of a button or a button fastener; a button or a button as a button group with a cap, and a method for forming such a button or a button fastener.
As a button or a button fastener, one type is known which includes a main body for a button or a button fastener and a cap (also referred to as a shell) which is attached to the main body. An outer surface of the cap becomes a front surface of a button or a button fastener, on which a design such as characters, logos and the like may be printed or impressed. One example of a button having such a cap is disclosed in JP,S63-22107,U, for instance. This document shows a shell member 4 as a cap in FIG. 1. Such a cap is attached to a button main body by swaging a circumferential side of the cap against the main body (a button back member 3 in FIG. 1 of the document). As mentioned above, since the outer surface of the cap becomes the front surface of the button or the like, the cap is typically made of copper or copper alloy that is relatively hard to scratch. However, in a case of the cap made of copper or copper alloy, spring back tends to occur when the circumferential side of the cap is swaged to the main body using a die or the like. In the spring back, the deformed circumferential side is somewhat returned toward its original state when the die or the like is removed. For this reason, there is a fear that a coupling force of the cap to the main body would be weaken over time. In this case, the cap would be rotated with respect to the main body. Under this situation, if a design of oriented characters and the like is drawn on the outer surface of the cap, namely, the front surface of the button, and this button is attached to clothing or the like in a predetermined orientation, there would be a problem that a rotation of the cap causes the orientation of the design to be displaced. To solve the problem, JP,S63-22107,U as mentioned above suggests a technique that adds a separate reinforcement member (10) to a cap (shell member 6). (refer to FIGS. 3 and 4 of the gazette).
However, the addition of a separate member to the cap increases the number of parts and consequently leads to a cost rise. Further, a process for manufacturing a button and the like would be complicated. In addition, a material cost of copper or copper alloy is expensive relatively to aluminum or aluminum alloy. However, though aluminum or aluminum alloy is relatively hard to induce a spring back, there would be a problem that the outer surface of a cap is easy to scratch.    [Patent Document 1] JP,S63-22107,U